Self-expanding rib



May 21, 1968 D. MCGEE 3,384,328

7 SELF-EXPANDING RIB Filed April 15, 1966 I NVEN TOR. DONOVAN M GEE 77f17 M4 mm/ ATTORNEYS United States Patent 3,384,328 SELF-EXPANDING RIB Donovan McGee, Northiield, Minn, assignor to G. F. Schjeldahl (10., Northfield, Minn., a corporation of Minnesota Filed Apr. 15, P366, Ser. No. 542,966 4 Claims. (61. 244-31) ABSTRACT OF THE DISCLOSURE A thin walled inflatable enclosure comprising a shell adapted for super pressure inflation and having at least one semi-rigid rib disposed along a surface thereof and extending along a substantial portion of the periphery, the rib comprising a structure formed from a pair of legs intersecting at an apex and secured at their respective bases to a surface of the super pressure inflatable enclosure, the distance between the bond lines being substantially less than the sum of the height dimensions of the legs so as to form a rib structure disposed in protruding relationship from the surface upon application of tension stresses to the enclosure along the area between the bond lines, the ribs being free of any inflation means.

The present invention relates generally to an improved means for increasing the structural rigidity of a thinwalled inflatable enclosure, such as, for example, a balloon or a similar inflatable structure, and more specifically to a means for increasing the structural rigidity of such an apparatus by means of providing a rib which becomes expanded or erected upon inflating the enclosure member per se.

In an inflatable structure, it is frequently desirable to increase the structural rigidity in order to render the inflatable more stable during flight. Furthermore, it is sometimes desirable to provide external protrusions on the surface of an inflatable structure, these protrusions having a reasonably regular pattern, for the purpose of stabilizing the flight characteristics of an inflatable load-carrying device such as a balloon or the like. For purposes of providing rigidity to the structure, the globe means may be provided either internally or externally of the structure, while for stabilizing the flight characteristics of the inflatable structure due to the presence of any turbulence in the atmosphere through which the device is being flown, it is necessary to arrange these protrusions externally of the structure.

In addition to the structural rigidity and flight stability considerations, one must carefully consider the addition of weight to the inflatable, as Well as any increase in packing volume. It wi l be readily appreciated that any addition of weight to the inflatable structure will constitute a corresponding decrease in the load-carrying capability of the structure. Also, any increase in packing volume will be considered detrimental to the overall structure. In accordance with the present invention, this increase in rigidity is provided with a minimum increase in weight for the inflatable, and also with a minimum increase in packing volume.

An additional consideration is the erecting capability of any structural member added to the inflatable. Inflation problems are sulficiently complex to make it undesirable to compound these problems to any extent by requiring separate inflation means for the protruding ribs.

In accordance with the present invention, these ribs are self-expanding in nature and accordingly do not require any auxiliary inflation means.

Briefly, in accordance with the present invention, a self-expanding rib is provided for mounting on the wall of a thin-walled inflatable structure such as a load-carrying balloon or the like. The rib is fabricated from a web or strip of material which is bonded to the wall of the inflatable along substantially parallelly disposed spaced bond lines. The distance between the bond lines is substantially less than the width of the web of material, so that the web therefore forms a pair of legs which meet at an apex so as to form a rib structure which protrudes from the surface of the shell whenever tension is applied along the inflatable structure between the bond lines. As indicated, this is accomplished without requiring any auxiliary inflation means for the rib structures.

It is therefore an object of the present invention to provide a means of increasing the structural rigidity of a thin-walled inflatable, this added rigidity being provided with a minimum increase in packing volume and finished weight.

It is a further object of the present invention to provide a means of increasing the structural rigidity of a thin-walled inflatable by means of mounting a self-expanding rib along the surface of the inflatable member.

It is yet a further object of the present invention to provide a means of increasing the structural rigidity of a thin-walled inflatable and also improve the free-flight characteristics of such an inflatable by providing a selfexpanding rib structure along the external surface of the inflatable, this being accomplished with a minimum increase in packing volume and Weight.

Other and further objects of the present invention will become apparent to those skilled in the art upon a study of the following specification, appended claims and accompanying drawing wherein;

FIGURE 1 is a plan view, partially broken away, of a spherical inflatable device provided with self-expanding ribs along the internal surface thereof;

FIGURE 2 is an elevational view of a load-ca r ing balloon capable of free-flight which is provided with a plurality of externally disposed self-expanding ribs prepared in accordance with the teachings of the present invention;

FIGURES 3(a) and (b) are detail cross-sectional views of typical rib structures which may be used in accordance with the technique of the present invention, these rib structures being shown on a somewhat enlarged scale;

FIGURE 4 is a series of views of the rib structure shown in FIGURE 3(a), this series showing the manner in which the rib structure may be folded from an inflated condition to a delated or relaxed condition; and

FIGURE 5 is a series of views similar to that of FIGURE 4, and showing the manner in which the rib structure becomes erected upon inflation of the thinwalled inflatable structure.

In accordance with the preferred modification of the present invention, particularly as shown in FIGURES l and 2, an inflatable structure is shown having a plurality of self-expanding ribs which extend along a substantial portion of the periphery of each of the enclosures. With specific reference to FIGURE 1, the inflatable structure shown at 10 comprises a thin-walled body 11 formed from a plurality of gores bonded together along the joints formed therebetween by the seal tape 12. Therefore, the

shell comprises a plurality of spherical shell gore segments bonded together along the seams 12. Details of the seam are shown at FIGURE 3(a) and 3(1)). The thin-walled material forming the shell 11 is generally a film of polyethylene or polyethylene terephthalate, each of which is commercially available. If desired, for purposes of strength or the like, the surfaces may be provided with a skrim substance which will aid in preventing rupture of the surface of the thin-walled inflatable structure.

With continued attention being directed to FIGURE 1, the self-expanding rib structures are shown at ll313, in the broken away portion of the drawing. These ribs are formed either with a sharp apex as in FIGURE 3(a), or with a relatively smooth arcuate apex as shown in FIGURE 3(b). Generally, when the structure is folded in the manner shown in FIGURE 4, the apex will assume a relatively sharp bend or crease, and will be in the form shown in FIGURE 3(a). The legs of the rib structure are bonded to the inner surface of the thin-walled film 11, particularly as shown at 15 and 16. These areas form, in effect, the bond lines between the rib structure and the surface of the inflatable member. As is conventional on this type of structure, the individual gores meet at a cap area 14, and are there sealed together in a well known manner, either adhesive or thermal bonding techniques being employed.

The spherical structure it) shown in FIGURE 1 may be fabricated almost entirely from polyethylene or polyethylene terephthalate, as previously indicated. In addition, any suitable film material may be employed such as, for example, polypropylene or similar materials. If a substance is heat-sealable, such as polyethylene, a heat-sealable tape as shown at 12 may be employed to bond the material together in a butt-joint fashion. If a material such as polyethylene terephthalate is being employed, it is generally preferable to form the bond with an adhesive back tape. Such tapes are generally commercially available. When polyethylene is being utilized for a sphere having a diameter of, for example, 50 feet, a film thickness of about l-rnil would be considered appropriate, depending upon the ultimate application of the device. When polyethylene terephthalate is employed, the stressoriented variety is normally used, this being commercially available under the code name of Mylar, from the E. I. du Pont de Nemours & Co. of Wilmington, Del. For a similar spherical structure having a diameter of about 50 feet, stress oriented polyethylene terephthalate having a wall thickness of about /2 to 1 mil may be employed. For general application, the self-expanding rib should be at least semi-rigid. In this connection, stressoriented polyethylene terephthalate, when employed, should have a thickness at least comparable to the thickness of the walls of the inflatable structure. If desired, somewhat heavier gage material may be utilized, in order to achieve sufficient rigidity. For a sphere having a wall thickness of /2-mil, a rib of the same material having a comparable thickness has been found to be satisfactory.

Turning now to the load-carrying balloon structure shown in FIGURE 2, which structure has been generally designated 20, it will be observed that the wall members 21 are provided with a plurality of self-expanding ribs 22, which converge at a top-cap area 23, and a load ring 24. Thus, these ribs extend along a substantial portion of the periphery of the enclosure. The units formed in the wall members 21 are the same as those shown in FIGURES 3(a) and (b). The ribs, being externally disposed, enhance the free-flight stability characteristics of the structure whenever a turbulent condition is encountered. These ribs are formed in identical fashion to those described in connection with FIGURES 3(a) and (b), and as particularly described in connection with the apparatus of FIGURE 1. If desired, for purposes of joint stability, the tape member 12 may be arranged internally of the rib, however, for most purposes, it is generally desirable to provide this member on the side opposite that of the self-expanding rib in order to provide more ready access to this area in the event a repair is indicated.

The various views shown in FIGURE 4 illustrate the progress of the rib during a folding operation, that is, when the inflatable device is deflated, and being packed or stored, for one reason or another. It will be observed that the rib member is initially collapsed by bringing the two legs of the rib into virtual contact, one with another, such as is shown in the second and third figures of the sequence. The third figure of the sequence also shows the manner in which the rib, together with its adjacent area of wall structure, being folded flat against the wall surface. The last view in the sequence shows the rib in substantially folded or collapsed form and lying generally in contact with the surface of the shell. In an assembly which is being folded or stored, it has been found that these ribs contribute very little to the overall packed volume of the assembly.

FIGURE 5 is a view of the rib in a sequence similar to that of FIGURE 4, but showing the rib while it is being expanded from a packed or stored configuration. The various views, taken from left to right, show the configuration of the rib together with its associated wall surface, as it is being expanded or erected into its ultimate or desired configuration. The final view, that is, the view on the extreme right, shows the expanded configuration as it would exist in the sphere shown in FIGURE 1, the rib 13 being generally in the interior of the inflated member. Of course, the view could be taken from the balloon structure of FIGURE 2, however the seal member 12 would be preferably disposed on the same side of the film surface 11 as the self-expanding rib 13.

It will be appreciated that various materials of construction, together with various forms or configurations may be utilized in apparatus of this type. The ribs may run longitudinally of the inflated device, or transversely thereof, depending upon the ultimate requirements of the system. As previously indicated polyethylene, polyethylene terephthalate or polypropylene may be used as a structural material. In addition, a metalized material may be another possible material of construction. Like metal foils may also be usable.

It will be appreciated that the various examples given herein are for purposes of illustration only, and are not to be otherwise construed as a limitation upon the scope to which this invention is reasonably entitled.

What is claimed is:

1. A thin-walled inflatable enclosure comprising a shell adapted for super pressure inflation, said shell being comprised of a plurality of gores and having at least one semi-rigid rib disposed along a surface thereof and extending along a substantial portion of the periphery of said enclosure, said rib comprising:

(a) a pair of legs intersecting at an apex and secured at their respective bases to a surface of said enclosure along spaced apart bond lines, the distance between said bond lines being substantially less than the sum of the height dimensions of said legs so as to form a rib structure disposed in protruding relationship from said surface upon application of tension stress along the shell area between said bond lines said ribs being free of any inflation means,

(b) each of said gores being bonded together along edge surfaces with an overlapping bonding tape disposed along the oppositely disposed surface of said shell from said rib and along a line substantially midway between said spaced apart bond lines.

2. The thin-walled inflatable enclosure as defined in claim 1 being particularly characterized in that said legs are of equal height, and the distance between said bond lines is substantially equal to the height of said legs.

3. The thin-walled inflatable enclosure as defined in claim 1 being particularly characterized in that said semirigid rib is disposed on the interior surface of said shell.

5 4. The thin-walled inflatable enclosure as defined in claim 1 being particularlycharacterized in that said semirigid rib is disposed along the exterior surface of said shell.

References Cited UNITED STATES PATENTS 6 3,138,348 6/1964 Stahmer 244-146 X 3,277,724 10/1966 Lundeberg 244-31 X 3,279,419 10/1966 De Marco 244-33 X FERGUS S. MIDDLETON, Primary Examiner.

MILTON BUCHLER, Examiner.

T. MAI OR, Assistant Examiner. 

